TRAI does not explicitly define the restrictions in place. TRAI regulates that IP to PSTN calls should not result in a toll bypass resulting in loss of revenue to the ISP. As long is this is taken care of, calls should be legally allowed.
My advise would be to talk to your service provider. As for your scenario above, office VoIP infra should be restricted to office premises only. I cannot have Jabber etc logged in from my home and use my office PSTN line to make calls.
